An oligomer of olefins is used for many purposes and especially a dimer of low molecular olefins (for example, propylene, n-butene, isobutene, pentenes) has importance as a base material of the high-octane number base materials for gasoline production and a chemical intermediate product. An oligomerization including a dimerization of the olefin is conducted by the use of an acid catalyst where many studies have been conducted up to the present. The acid catalysts such as sulfuric acid, hydrogen fluoride, phosphoric acid, aluminum chloride, and boron fluoride, and a solid acid such as amorphous or crystalline aluminum silicate, clay, ion exchange resin, oxide mixture, and an acid supported on carrier are given as conventional examples, and many studies on the solid phosphoric acid which can provide an inexpensive and convenient production process, have been conducted.
For example, the oligomerization method of propylene by using the solid phosphoric acid prepared under the calcination condition of 100° C. or more (Reference Patent Document 1) and the oligomerization method of propylene by using the catalyst (catalyst comprising silicone orthophosphate and silicone pyrophosphate) which is prepared by a crystallization of an amorphous mixture of the phosphoric acid and siliceous raw material under the condition of 250°-450° C. and the steam concentration 3-50 mole % (Reference Patent Document 2), have been disclosed.
Also, a condensation degree of the phosphoric acid in the solid phosphoric acid catalyst has been known to influence on the activity of the oligomerization reaction of the olefin since early times, and for example, example of the oligomerization of olefins such as C3 and C4 and others using supported phosphoric acid catalyst with small weight ratio of free phosphoric acid to the catalyst are disclosed. The free phosphoric acid are designated as can be eluted by immersing the catalyst in water (correspond to non-condensed or low-condensed phosphoric acid such as orthophosphoric acid and pyrophosphoric acid). Ratio of H2O/P2O5 of such the supported phosphoric acid catalyst mentioned above corresponds to 31 mass % or less as the phosphoric acid composition. (Reference Patent Document 3, Non-Patent Document 1).
Also, according to the Reference Patent Document 3, the physical performance of the catalyst is made to deteriorate when the solid phosphoric acid catalyst is hydrated excessively, so that the hydration of the catalyst is controlled so as to make the predetermined level (corresponds to the above mentioned phosphoric acid composition) by feeding the raw material containing an adequate amount of water after conducting drying of the catalyst by hydrocarbon without containing a substantial amount of water.
However, the above mentioned methods of the oligomerization of the olefin by using conventional solid phosphoric acid catalyst are not targeted mainly to the dimerization of the olefin, and moreover, a highly polymeric product of the olefin as by-product can not be avoided by using the conventional solid phosphoric acid catalyst, so that it is difficult to obtain the olefin dimer selectively. Also, the conventional solid phosphoric acid catalyst is required to supply to the reaction in the state of small proportion of H2O/P2O5 as the phosphoric acid composition, so that there are various inconveniences such that the water contents control is required to conduct severely so as to make water contents in the predetermined amount while preparation and storage of the catalyst (making surplus water in the catalyst so as to be small) and also drying step of the catalyst is required before the reaction.
Reference Patent Document 1: JPH08-29251B
Reference Patent Document 2: JPH07-59301B
Reference Patent Document 3: JP2001-199907A
Reference Non Patent Document 1: “Applied Catalysis A: General”, 1993, 97, p. 177-196.